1. The scientific study of sleep has recently been stimulated by comparisons between people and advanced computers, whose normal activities need to be suspended periodically for reprogramming. I quote from a popular account by Dr Christopher Evans, which appeared in the Sunday Times during 1969:

Sleep is of course the state in which the brain-computer is ‘off-line’, during which time the vast mass of existing programmes are sorted, outdated ones revised in the light of recent experiences and useless ones or the remnants of modified ones cleared and eliminated. These processes take place for a substantial part of the night, but because the brain is ‘off-line’ and consciousness suppressed, we are mostly not aware of them. However, if for some reason our sleep is disturbed or when we wake in the morning, as the conscious mind ‘comes to’ it catches the programme operations at work, and for a moment has no way of knowing whether the events are internal or external in origin. It sets to work therefore to try to make sense of the programme or fragments thereof that are being run through, and the result is what we call a dream— though we should presumably call it an interrupted dream.